A planer mill is a woodworking operation of the type used in large volume lumber manufacturing. A planer mill typically includes a number of individual machines grouped together in a production line setting. One of the key machines in a planer mill is a planer unit, or "planer-matcher", a device which planes wood to predetermined dimensions; i.e. smoothes or levels flat or uniformly contoured surfaces of wood using relatively wide edged blades. The planer-matcher often works in combination with other machines positioned in the production line, such as circular saws, band saws, or log gang saws and related machines, and to which the planer-matcher is connected by chain or belt conveyors.
Typically, a planer-matcher can operate at a faster speed than some of the other units in a woodworking or lumber mill. As a result, the planer can operate no faster than the speed of the slowest unit in the production line Stated differently, some other portion of the mill usually represents the rate determining step. If the planer were to operate at a speed faster than the speed of the slower conveyor unit for example, the planer would produce an overabundance of planed wood, resulting in a jam-up. Under such circumstances, which tend to occur in manually operated plants, an operator then must stop the production line and remove the jam. This can be costly in terms of production. For example, if such a line stops for ten minutes, and the planer operates at a feed rate of about 100 pieces of wood per minute, such a jam-up and the related down time would account for a productivity drop of 1,000 pieces of planed wood that otherwise could have been manufactured during that time period.
In general, planers are usually operator controlled. The operator observes the general rate at which wood pieces or boards are being fed into and out of the planer and then uses a potentiometer or similar control to either speed up or slow down the planer-matcher to obtain a desired rate. This technique offers a number of disadvantages, however, particularly the lack of precise control over the speed of the planer-matcher. As stated above, if wood is being treated by the planer-matcher at rates of up to 100 pieces per minute, an operator may experience difficulty in estimating and hand-controlling the speed of the planer-matcher in an attempt to maintain a speed that both prevents downstream jam-up of planed wood, while at the same time speedily working all of the wood being fed into it without causing input delays.
Therefore, the need exists for a more precise control of a planer-matcher in a manner which moderates the differences in speed that can occur during overall mill operations, while avoiding the inherent difficulties in trying to do so manually.